title: Solution structure of the epidermal growth factor (EGF)-like module of human complement protease C1r, an atypical member of the EGF family.
abstract: The calcium-dependent interaction between C1r and C1s, the two homologous serine proteases of the first component of human complement C1, is mediated by their N-terminal regions. The latter comprise an epidermal growth factor (EGF)-like module exhibiting the consensus sequence characteristic of Ca(2+)-binding EGF modules, surrounded by two CUB modules. Due to its Ca2+ binding ability, the C1r EGF-like module (C1r-EGF) is supposed to participate in the C1r-C1s interaction. An additional interesting feature of C1r-EGF is the unusually large loop connecting the first two conserved cysteine residues. The solution structure of synthetic C1r-EGF (residues 123-175) has been determined using nuclear magnetic resonance and combined simulated annealing-restrained molecular dynamics calculations. The resulting family of 19 structures is characterized by a well-ordered C-terminal part (residues Cys 144-Ala174) with a backbone rmsd of 0.7 A and a disordered N-terminal, including the large loop between the first two cysteines (Cys129 and Cys144). This loop is known to be surface exposed and may be expected to participate in domain-domain or protein-protein interactions. In its C-terminal part, C1r-EGF possesses the characteristic EGF fold with a major and a minor beta-sheet. The latter comprises a beta-bulge, and comparison with other EGF-like modules reveals the existence of two distinct structural and sequential motifs in the bulged part. Additional experiments in the presence of 80 mM Ca2+ did not show significant structural variation of C1r-EGF, in keeping with previous observations on blood-clotting factors IX and X.
authors.affiliation: Laboratoire de Résonance Magnétique Nucléaire, Institut de Biologie Structurale Jean-Pierre Ebel, CNRS-CEA, Grenoble, France.
authors.forename: B
authors.initials: B
authors.lastname: Bersch
authors.forename: J F
authors.initials: JF
authors.lastname: Hernandez
authors.forename: D
authors.initials: D
authors.lastname: Marion
authors.forename: G J
authors.initials: GJ
authors.lastname: Arlaud
mesh_terms: D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism; D015923:Complement C1r / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D004815:Epidermal Growth Factor / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D017433:Protein Structure, Secondary; D012697:Serine Endopeptidases / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D012996:Solutions
chemical_list: D012996:Solutions; D004815:Epidermal Growth Factor; D012697:Serine Endopeptidases; D015923:Complement C1r; D002118:Calcium